This disclosure generally relates to a gas turbine engine including three spools. More particularly, this disclosure relates to a bearing arrangement for supporting rotation of each of the three rotating spools.
A gas turbine engine includes a core section that draws airflow into a compressor that compresses incoming airflow, and feeds the compressed air into a combustor. In the combustor fuel is added and ignited to generate a high speed flow stream that creates thrust and is exhausted through a turbine. A core section typically includes a low spool that includes a low pressure compressor section and a high spool that includes a high pressure compressor section. The low spool is typically driven by turbine blades within a low pressure turbine section and the high spool is driven by turbine blades within a high pressure turbine section. The different spools provide for different rotational speed between the spools to improve engine efficiencies.
It is further known to include an intermediate spool to further provide improvements in engine efficiencies by rotating at still another speed than both the low spool and the high spool. The addition of the intermediate spool complicates bearing arrangements as additional lubricant and cooling passages are required for the additional bearings required to support the intermediate spool. Typically, the intermediate spool and the high spool are supported by a hot strut disposed just aft of the combustor section. The hot strut is exposed to hot combustion gases. Therefore, cooling of the strut and the lubricant passages through the strut for the bearings is required to maintain lubricant at a desired temperature to prevent lubricant degradation. Moreover, the hot strut increases the overall length of the engine. The required hot strut therefore creates high demands on lubricant and cooling of bearings and limits placement choices of engine architecture.